Lesson 8: 5-5: The Triangle Inequality
Duration of Days: 2
Lesson Objective
1. Use the Triangle Inequality Theorem to identify possible triangles.
2. Prove triangle relationships using the Triangle Inequality Theorem.
1. What are some characteristics of triangles?
2. What general statements can be made about the sides of a triangle?
G.CO.10
Prove theorems about triangles
G.MG.3
Apply geometric methods to solve design problems (e.g., designing an object or structure to satisfy physical constraints or minimize cost; working with typographic grid systems based on ratios).
The Triangle Inequality Theorem states that the sum of the lengths of any two sides of a triangle is greater than the length of the third side. This theorem is used to determine whether three segments with given lengths form a triangle.
On a home improvement show, a designer wants to use scrap pieces of cording from another sewing project to decorate the triangular
Students approaching grade level can be given practice problems in small groups to work with other students or directly with the teacher.
Students beyond grade level can make deeper connections by determining the range of lengths that would be acceptable for the third side of a triangle when given the lengths of the two other sides.
Formative Assessment
Textbook in class
Access online textbook and resources through class link.